4.1 'sees' my USB drive but 4.2 doesn't

4.1 'sees' my USB drive but 4.2 doesn't

My daughter has a heap of baby videos on a USB stick. I can play these easily with File Manager on my phone running 4.1 .
But on her phone running 4.2, File Manager doesn't even see it.
So I downloaded Total Commander and USB-stick Plugin. Once again I had complete success with 4.1 and none with 4.2.

Any thoughts, suggestions as to why this should be and how to fix or work around it would be greatly appreciated.